Not since 1994 has New Hampshire voted to send a Democrat and a Republican to the House in the same election, but several factors have converged this cycle to make that outcome a distinct possibility.

The reasons that many Granite State political observers are preparing for a split delegation are plenty. There is no national wave; as House race veterans, the candidates are already well-known and defined; both parties are overloading the television airwaves with political advertising; and polling indicates the presidential race is tightening.

“It’s certainly possible,” a New Hampshire Republican said.

Each race is a 2010 rematch. Rep. Frank Guinta (R) is fighting off former Rep. Carol Shea Porter’s (D) attempt to win back the 1st district, while attorney Ann McLane Kuster (D) is taking another swing at Rep. Charles Bass (R) in the 2nd district. But rematches aside, these are two very different contests.

Both parties insist they can carry both seats. Still, Democrats are more confident about their prospects in the 2nd district, while Republicans are more upbeat about holding the 1st district.

Democrats have released several promising surveys that show Shea Porter up over Guinta. But Republicans shrug them off, saying they see Guinta up in their own internal polls.

Shea Porter has been universally perceived as a weak candidate who could only get to Congress in a Democratic wave year. The rap on her is that she is a terrible fundraiser. Guinta consistently outraised her this cycle, according to disclosure reports. But in the third quarter, Shea Porter raised nearly $700,000 and almost achieved cash-on-hand parity with Guinta.

“Carol’s huge quarter is a clear sign that New Hampshire is sick of Congressman Guinta’s tea party record and that she’s on her way back to Congress,” Democratic Congressional Campaign Committee spokesman Josh Schwerin said.

After losing in the Democratic wave of 2006, Bass launched his political comeback in 2010. He beat Kuster in what turned out to be another wave — this one benefiting the GOP.

Democrats say they saw the Republican wave coming in New Hampshire but remained confident until the end that Kuster would be their one bright spot of news that year.

“That was the heartbreak of the cycle as far as I’m concerned,” a national Democratic operative involved in the race said.

Even though Bass is perceived to be in serious trouble again this year, the National Republican Congressional Committee is so far hanging in there with him, with no evidence of overconfidence among Democrats.

“He’s not an easy target, but Kuster runs a really great shop,” the Democratic operative said.

Democrats have sought to tie Bass to national conservatives, but he has long cultivated a reputation as a New England moderate who frustrates some in the party.

Some Democrats blame Kuster’s 2010 loss on now-Sen. Kelly Ayotte (R) and her 23-point victory over then-Rep. Paul Hodes (D). Not everyone agrees with that theory, but the calculation was that Ayotte’s coattails propelled Bass and sunk Kuster.

Ayotte is not on the ballot this year, but President Barack Obama and Republican presidential nominee Mitt Romney are.

Analysts say the presidential contest is a tossup here. But regardless of who wins, the result could help contribute to voters splitting their House delegation.

The Senate delegation is currently split between Ayotte and Sen. Jeanne Shaheen (D), who was elected in 2008.

Republicans are confident Romney will win Guinta’s 1st district, and Democrats share a similar confidence that Obama will carry Bass’ 2nd district.

In the 1st district especially, it is hard to imagine much crossover voting. Guinta and Shea Porter are often described as fierce partisans, and as a result, this is a district where the presidential contest will matter more than most.

Obama won both districts in 2008, but Republicans insist that 2008 was an anomaly and not an indicator of future performance. And 2010 at least partially proved that when Democrats lost both seats.

Money matters in this race because television advertising rates are expensive. The majority of voters in the 1st and 2nd districts share the Manchester media market, which is served by one network affiliate based there, as well as Boston’s network affiliates.

According to a source tracking New England media buys, it has been “a record year” for anyone selling television advertisements in New Hampshire or Massachusetts, which reaches Granite State voters.

One Democrat estimated that one out of every five commercials on the New Hampshire and Boston airwaves were political. A GOP source described that estimate as “low.”

Correction, Oct. 25

An earlier version of this story incorrectly stated the amount of money raised by Carol Shea Porter during the third quarter. She raised almost $700,000.